The present invention relates to a process for producing a coated molded body in which at least one layer of hard materia, comprising at least one carbide, nitride or carbonitride of at least one of the elements titanium, zirconium, hafnium, niobium and tantalum is deposited on a metallic substrate from a reactive gas phase, according to the chemical vapor deposition (CVD) process. Such molded bodies have good anti-wear properties. Thus, they are used, in particular, as tools for chip-producing and chipless shaping of metallic work pieces.
A molded body, comrprising ahard metal substate and at least one layer of hard metal, is known from Swiss Pat. No. 507 904, in which the hard metal substrate is composed of one or more hard materials and at least one binder metal and in which the layer of hard material contains hard carbides or nitrides. Such molded bodies may be used as tools for chip-producing and chipless shaping, since they have good anti-wear properties. The well-known molded bodies are produced according to the CVD process (chemical vapor deposition process), as described in the Swiss Pat. No. 452 205. In the CVD process, which currently belongs to the usable coating methods, a surface layer is deposited on a substrate from a reactive gas atmosphere, whose temperature usually ranges from 600.degree. to 1200.degree. C. The gas atmosphere contains several compounds, which react with one another at the reaction temperature and form the material which comprises the surface layer. For example, the general practice is to coat metallic substrates with layers of hard material, consisting of carbides, nitrides, or carbonitrides, whereby the gas atmosphere contains halides of the group III to VI elements of the periodic system and a nitrogen-containing compound and/or a carbon-containing compound. Thus, for example, a layer of titanium carbide is deposited on a hard metallic substrate from a gas atmosphere, which contains titanium tetrachloride and methane, at approximately 1000.degree. C. Suitable carbon-containing compounds which can be used in the gas atmosphere generally are gaseous hydrocarbons, whereas suitable nitrogen-containing compounds may be N.sub.2, NH.sub.3, or amines.
It has been shown that the deposition of hard carbides, nitrides and carbonitrides on metallic substrates according to the CVD process requires quite a long reaction time, since the deposition speed is approximately 1 to 2 .mu.m/h, and that the layers of hard material have too coarse a grain structure, which reduces their adhesion and resistance to wear. Since as a rule the layers of hard material should have a thickness, ranging from 8 to 12 .mu.m, it is necessary that the layers of hard material have a fine grain structure.